Facilitating data compression during replication using a compressible configuration bit

ABSTRACT

A method is provided for facilitating data replication in a storage system. A logical volume of a first storage array of a replicated pair is preconfigured with one or more logical volume attributes, which include a compressible configuration bit that indicates whether data blocks to be stored to that logical volume are compressible during replication. Subsequently, with receipt of a data block at the first storage array to be stored to the logical volume, a check of the compressible configuration bit is made to determine whether the data block is compressible during replication, and if so, the data block is compressed for replication. The compressible configuration bit is placed into the payload region of the data packet being replicated to the second storage array. At the second storage array, the compressible configuration bit is used to determine whether to uncompress the replicated data block.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 12/607,118, entitled“FACILITATING DATA COMPRESSION DURING REPLICATION USING A COMPRESSIBLECONFIGURATION BIT,” filed Oct. 28, 2009, and published Apr. 28, 2011, asU.S. Patent Publication No. 2011/0099344 A1, and which is herebyincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates in general to storage systems, storagecontrollers and data compression, and more particularly, to facilitatingdata compression during replication between storage arrays of a storagesystem.

In recent years, storage area networks (SANs) have become popular. In astorage area network, the storage units (or storage devices) are notlocally attached to a particular host, but rather are connected to ahost or series of hosts through a switch fabric, where each host canaccess each storage unit. In this manner, multiple hosts may sharestorage units so that storage space can be more readily allocatedbetween the applications on the host(s).

In one example, a storage area network manages a plurality of diskdrives arranged in an array according to a RAID (Redundant Array ofIndependent Disks) configuration. One or more logical volumes are formedin a physical storage array provided by the plurality of disk drives,and these logical volumes are provided to the host system(s).

Since this type of storage system handles large volumes of data, datacompression is often employed (e.g., during replication) to increaseperformance of data transfer rates beyond a default rate foruncompressed data itself. Certain existing storage controllerimplementations utilize an all-or-nothing approach to compressing databefore transferring data across a link. If compression is activated,then the storage controller attempts to compress every frame of data,whether it is compressible, non-compressible or already compressed. Theresult can be degradation in data transfer rates due to lost performancefrom, for example, attempting to compress non-compressible frames ofdata, prior to transfer of the data across the link.

BRIEF SUMMARY

In one aspect, a method of facilitating replication of data in a storagesystem is provided. The method includes: configuring a logical volume ofa storage unit of a first storage array of the storage system with atleast one storage volume attribute, which comprises a compressibleconfiguration bit, the compressible configuration bit indicating whetherone or more data blocks to be stored to the logical volume arecompressible during replication. Receiving a data block at the firststorage array to be stored to the logical volume of the storage unit;and checking the compressible configuration bit associated with thelogical volume, and based thereon, determining whether to compress thedata block during replication thereof from the first storage array to asecond storage array of the storage system.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram illustrating one embodiment of a storagesystem to utilize a data compression and replication facility, inaccordance with an aspect of the present invention;

FIG. 2 is a block diagram of one embodiment of a storage controller ofthe storage system of FIG. 1, in accordance with an aspect of thepresent invention;

FIG. 3 is a block diagram illustrating two storage arrays logicallycoupled via a replication link, and utilizing a data compression andreplication facility, in accordance with an aspect of the presentinvention;

FIG. 4 depicts one embodiment of a process for facilitating dataemploying a compressible configuration bit, in accordance with an aspectof the present invention;

FIG. 5 depicts one example of a data packet format for replication andillustrating a compressible configuration bit inserted into the datapayload region of the data packet, in accordance with an aspect of thepresent invention; and

FIG. 6 depicts one embodiment of a computer program productincorporating one or more aspects of the present invention.

DETAILED DESCRIPTION

Reference is made below to the drawings (which are not drawn to scalefor ease of understanding), wherein the same reference number is usedthroughout different figures to designate the same or similarcomponents.

FIG. 1 depicts one embodiment of a data storage system 100 comprising astorage area network. Central to the storage area network is one or morestorage area network (SAN) fabrics 110, each of which is formed of aseries of routers or switches, such as Fibre Channel switches accordingto the Fibre Channel specifications. These switches are interconnectedto provide a full mesh (or fabric), allowing any node to connect to anyother node. Various nodes and devices can be connected to SAN fabric110. For example, a plurality of host systems 120 are typically coupledto SAN fabric 110 to communicate through the fabric to other devices.These other devices include one or more storage arrays 130 (describedbelow). In addition, a management server 140 is shown connected to SANfabric 110 for managing storage arrays 130. In an alternate embodiment,a local area network could be employed to couple the management server140 to storage arrays 130, without relying on SAN fabric 110.

Each host system 120 is a computer device comprising informationprocessing resources such as a central processing unit and memory, andmay be configured, for example, from a personal computer, workstation,mainframe, etc.

FIG. 2 illustrates one embodiment of a storage array 130 of a storagesystem, such as depicted in FIG. 1. As illustrated, storage array 130 isconnected to storage area network (SAN) fabric 110, and includes astorage controller 200, and a storage unit 210. Storage controller 200comprises, in the illustrated embodiment, a frontend interface 201, adata transfer controller 202, a CPU 203, local memory 204, cache memory205 and a backend interface 206. As shown, data transfer controller 202includes a compression controller 207 (which is distinct from anencryption/decryption controller (not shown), which also mayconventionally be included within the data transfer controller of thestorage controller).

Storage controller 200 controls a plurality of storage modules ofstorage unit 210, such as a plurality of hard disk drives 211. In oneexample, control of the storage unit is based on a RAID level defined ina so-called RAID system. In an RAID system, a plurality of hard diskdrives 211 are managed as a single RAID group. A plurality of logicalvolumes 212 are defined in the RAID group as access units from the hostsystem 120 (FIG. 1). A LUN (logical unit number) is allocated to eachlogical volume 212.

Frontend interface 201 is a controller for controlling the interfacewith one or more host systems and, for instance, has a function forreceiving a data block input/output (I/O) request from a host systembased (for example) on the Fibre Channel protocol. Frontend interface201 further includes controls for sending and receiving control signalsto and from the management server of the storage area network. CPU 203is a processor which controls a write access or read access to theplurality of hard disk drives 211 in response to a data I/O request froma host system. Further, CPU 203 executes processing according to variouscommands sent from the management server 140 (see FIG. 1), and theprocessing of programs stored in local memory 204. Local memory 204stores various types of data and programs to facilitate control of thestorage array 130.

Data transfer controller 202 connects cache memory 205, frontendinterface 201, backend interface 206, and CPU 203. Data transfercontroller 202 again includes compression controller 207, and controlsthe data transfer between a host system (see FIG. 1) coupled to the SANfabric 110 and the hard disk drives 211 of storage unit 210.

Cache memory 205 is a buffer memory for temporarily storing write datato be written into the hard disk drives 211, read data being read fromthe hard disk drives 211 and data to be sent to the cache memory ofanother storage controller during a replication operation. Compressioncontroller 207 is a controller for reading and compressing (oruncompressing) data temporarily stored in cache memory 205.

Backend interface 206 is a controller for controlling the interface withthe hard disk drives 211, and for instance, has a function ofcontrolling the data I/O requests to the hard disk drives 211 based on aprotocol for controlling the hard disk drives.

Hard disk drives 211 are storage devices configured, by way of example,from FC (Fibre Channel) disk drives, SATA (Serial Advanced TechnologyAttachment) disk drives, PATA (Parallel Advanced Technology Attachment)disk drives, FATA (Fibre Advanced Technology Attachment) disk drives,SAS (Serial Advanced SCSI) disk drives, SCSI (Small Computer SystemInterface) disk drives, etc.

Referring to FIG. 1, management server 140 is, for instance, a computersystem comprising hardware resources such as a CPU, a memory and adisplay. Employing management server 140, input operations may beperformed by a system operator. The system operator is able to sendcommands for managing one or more of the storage arrays. These commandsmay include, for example, a command for increasing or decreasing thenumber of hard disk drives 211, or changing the RAID configuration, acommand for installing the CPU's micro-programs in local memory, acommand for confirming the operational status of a storage array, or acommand for defining one or more logical volumes 212 within storage unit210.

In one embodiment, each storage array 130 is configured as describedabove in connection with the storage array depicted in FIG. 2. When awrite access is requested from the host system, data transfer controller202 foremost writes the data received from the host system via frontendinterface 201 into cache memory 205. Subsequently, data transfercontroller 202 transfers the data to backend interface 206 in order toperform asynchronous writing to the hard disk drives 211. When readaccess is requested from the host system, data transfer controller 202writes the data read from the hard disk drives 211 via backend interface206 into cache memory 205, and subsequently transfers the data to thefrontend interface 201. Frontend interface 201 then transfers thecompressed data to the requesting host system.

For data availability, data replication is often employed within astorage system such as depicted in FIGS. 1 & 2. Data replication occursbetween preconfigured replication pairs of storage arrays of the storagesystem (e.g., between replication pairs of logical volumes), and isgenerally, a point-to-point transfer of data from one storage array toanother storage array. When possible, data compression increases datatransfer rates during replication beyond a default rate for uncompresseddata. However, the types of data that can be compressed vary. Certainstorage controllers available today utilize an all-or-nothing approachto compressing data during replication from one storage array to anotherstorage array. For example, EMC Corporation, headquartered in Hopkinton,Mass., USA, offers a Symmetrix DMX-4 series high-end storage system withstorage controllers that have a built-in capability to automaticallyattempt to compress data during replication. However, when compressionis enabled, such storage controllers attempt to compress every datablock, whether it is compressible or non-compressible. The storagecontroller has no knowledge or any way of determining whether or not thereplicated data is compressible for replication.

Presented herein is a solution. Specifically, a data compression andreplication facility is disclosed, which provides the storage controllerwith processing intelligence to selectively compress a data block beingreplicated from a first storage array to a second storage array of thestorage system if it is in fact compressible. This ability to know whichdata blocks are compressible before attempting compression improves datatransfer rates between the storage arrays and thus, facilitates thereplication operation.

FIG. 3 illustrates a replicated pair of storage arrays in a storagesystem comprising (in one embodiment) multiple storage subsystems. Asillustrated, the replicated pair includes a first storage array 130A anda second storage array 130B, each coupled to storage area network fabric110. First storage array 130A and second storage array 130B are eachconfigured as described above in connection with the storage area arrayof FIG. 2, with reference “A” being added to the reference numerals forthe first storage array 130A, and reference “B” being added to thereference numerals for the second storage array 130B. In one embodiment,the first storage array 130A and the second storage array 130B are indifferent storage subsystems of a set of storage subsystems, that are inthe same, or more typically, different geographic locations.

In FIG. 3, first storage array 130A is shown to include atransmit/receive buffer 300A within data transfer controller 202A, andsecond storage array 130B includes a transmit/receive buffer 300B withindata transfer controller 202B. A replication link 310 couples (in oneexample) the transmit/receive buffers 300A, 300B. This replication link310 may comprise a physical link, or a logical representation of a link,for example, through SAN fabric 110. Further, although shown within datatransfer controllers 202A, 202B, the transmit/receive buffers 300A, 300Bmight reside elsewhere; for example, within the respective cachememories 205A, 205B of the storage controllers 200A, 200B.

As noted, during replication of a data block from first storage array130A to second storage array 130B, compression controller 207Aconventionally attempts (in an all-or-nothing approach) to compressevery data block being replicated. This slows the data transfer rate inthose cases where the data block is non-compressible data. To addressthis issue, a new bit, referred to herein as the compressibleconfiguration bit, is employed, both as a storage volume attributeassociated with a logical volume where the data block is to be stored,as well as part of a header string placed in the data payload region ofthe data packet being replicated from the first storage array to thesecond storage array. This use of the compressible configuration bit isdescribed further below with reference to FIG. 4.

In FIG. 4, a process is depicted for facilitating replication of data ina storage system. The process, which is described below with referenceto the storage system of FIG. 1 and the replicated pair of FIG. 3,includes configuring a logical volume of a storage unit of a firststorage array with one or more storage volume attributes that include acompressible configuration bit (STEP 400). For example, a systemadministrator might employ the management server 140 (see FIG. 1) toinstruct the first storage array to associate a new storage volumeattribute with one or more of the logical volumes of the storage unit ofthe storage array. This new storage volume attribute that includes thecompressible configuration bit may be set by the system administrator ONor OFF for each particular logical volume within the storage unit of thefirst storage array. Alternatively, the compressible configuration bitcould be ON or OFF by default for a particular logical volume, dependingupon the implementation. In the example described below, it is assumedthat the compressible configuration bit is set ON, that is, any datablock to be written to the particular logical volume is defined to becompressible during replication.

Subsequently, a write data block request is received at the firststorage array with a particular block address in one of the logicalvolumes of the storage unit of the first storage array. The write datablock request is received from a host system (in one example), throughthe SAN fabric to the first storage array 130A (see FIG. 3), intostorage controller 202A via frontend interface 201A. The data transfercontroller 202A then places the received data block into cache memory205A (STEP 410, FIG. 4).

Storage controller 200A (FIG. 3) checks the storage volume attributesassociated with the logical volume to which the data block is to bewritten, and determines whether the logical volume is part of areplication pair and (if so), whether to compress the data block duringreplication (STEP 420). Indicating that the logical volume is part of areplication pair is (in one embodiment) via the new storage volumeattribute associated with the logical volume (which includes thecompressible configuration bit that has been set as described above). Byway of example, assume that the compressible configuration bit is setON, meaning that any data block to be storated to that logical volume iscompressible during replication, and further, assume that the storagecontroller 200A has a default setting where the storage controller doesnot attempt to compress data blocks during replication. In this case,the compressible configuration bit being set ON means that the datablock will be compressed by the storage controller during replication.(Alternatively, the storage controller could be set by default tocompress data blocks automatically during replication, in which case thecompressible configuration bit could be used to override the automaticcompression for those data blocks that are non-compressible.)

As a further aspect, the replicated data can include an indication ofwhether the data block was compressed by the first storage array duringreplication to the second storage array. To accomplish this, the storagecontroller could either immediately place a compressible configurationbit in the data payload region of the data packet being assembled forreplication (e.g., wrapped in an appropriate string placed into the datapayload region of the packet), or set a bit in a trackable table for usein subsequently inserting a string into the data payload region of thepacket when assembling the data packet for replication. In one example,the data packet is a Fibre Channel packet assembled for transmissionacross a Fibre Channel replication link logically or physically couplingstorage controller 200A (FIG. 3) of first storage array 130A and storagecontroller 200B of second storage array 130B.

FIG. 5 illustrates one example of a compressible configuration bit 500(e,g., inserted as a reference string) into the data payload region 510of a data packet frame 520 being replicated from the first storage arrayto the second storage array. In this example, it is assumed that thedata packet is a Fibre Channel (FC) data packet being transmitted acrossa Fibre Channel link. This implementation, however, is provided by wayof example only. Note that, conventionally, the frame header informationresides outside of the data payload region of the data packet, asdefined by existing Fibre Channel specification. In accordance with thepresent invention, however, the reference string containing thecompressible configuration bit is inserted into the data payload region(specified by the packet protocol to receive the data block), andtherefore, no change to the existing packet header configuration isrequired, e.g., no change to the existing Fibre Channel specification isrequired to implement the present invention.

Continuing with FIG. 4, when the logical volume into which the datablock is to be placed is part of a replication pair, and the logicalvolume is configured with a compressible configuration bit set forcompression of the data block during replication, the storage controllerschedules the data block for actual replication on a link and assemblesthe data block into a data packet for replication on the link (STEP430). This assembling includes (in this example) compressing the datablock and placing the compressed data block in the data payload regionof the data packet, along with the compressible configuration bit (asillustrated in FIG. 5) (STEP 440, FIG. 4). In one embodiment, the datapacket is placed into the transmit/receive buffer 300A (FIG. 3) of thestorage controller for transmission of the data packet over replicationlink 310 to second storage array 130B, and in particular, totransmit/receive buffer 300B of data transfer controller 202B of storagecontroller 200B.

Data transfer controller 200B (FIG. 3) of the second storage arrayreceives the data packet into cache memory 205B (STEP 450, FIG. 4), andchecks whether the compressible configuration bit in the referencestring in the data payload region of the data packet indicates that thedata block was compressed prior to replication (STEP 460). The storagecontroller strips the compressible configuration bit from the payloadregion, and if the data was compressed during replication, uncompressesthe data block prior to placing the data block on the de-staging queuein the second storage array for writing of the data to storage unit 210B(FIG. 3) of the second storage array 130B (STEP 470, FIG. 4).

Those skilled in the art will note from the above description that thedata block replication facility presented herein provides processingintelligence to the storage controller that allows the storagecontroller to avoid, for example, attempting to compressnon-compressible data blocks during replication. Data that is determinedto be compressible via the compressible configuration bit associatedwith the logical volume to which the data is to be stored willautomatically be compressed by the storage controller beforereplication, while data that is non-compressible (as determined by thecompressible configuration bit) can immediately be transmitted throughthe replication link, thereby enhancing replication rates. Thecompressible configuration bit described herein is both a storage volumeattribute associated with the logical volume to which a data block is tobe stored, and part of a reference string placed into the data payloadregion of the data packet assembled during replication of the data blockfrom the first storage array to the second storage array of areplication pair. Advantageously, the data block replication facilitydescribed herein is independent of various implementations of the FibreChannel standard or other link standards.

In an alternate implementation, the data storage system may ensure thatreplicated logical volume pairs are guaranteed to always have matchingcompressible configuration bit attributes. This would require that therebe no window of time in which the compressible configuration bitsassociated with the logical volumes in the replicated logical volumepair mismatch. In such a case, the compressible configuration bit neednot be included as part of the reference string incorporated into thedata payload region of the packet assembled during replication of thedata block from the first storage array to the second storage array ofthe replicated pair. The second, receiving storage array in this examplewould check the storage volume attributes associated with its respectivelogical volume to determine whether the compressible configuration bitwas set, and then act accordingly on the received replicated data.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system”.Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readablestorage medium. A computer readable storage medium may be, for example,but not limited to, an electronic, magnetic, optical, or semiconductorsystem, apparatus, or device, or any suitable combination of theforegoing. More specific examples (a non-exhaustive list) of thecomputer readable storage medium include the following: an electricalconnection having one or more wires, a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, a portable compact disc read-only memory (CD-ROM), anoptical storage device, a magnetic storage device, or any suitablecombination of the foregoing. In the context of this document, acomputer readable storage medium may be any tangible medium that cancontain or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Referring now to FIG. 6, in one example, a computer program product 600includes, for instance, one or more computer readable media 602 to storecomputer readable program code means or logic 604 thereon to provide andfacilitate one or more aspects of the present invention.

Program code embodied on a computer readable medium may be transmittedusing an appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programminglanguage, such as Java, Smalltalk, C++ or the like, and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

In addition to the above, one or more aspects of the present inventionmay be provided, offered, deployed, managed, serviced, etc. by a serviceprovider who offers management of customer environments. For instance,the service provider can create, maintain, support, etc. computer codeand/or a computer infrastructure that performs one or more aspects ofthe present invention for one or more customers. In return, the serviceprovider may receive payment from the customer under a subscriptionand/or fee agreement, as examples. Additionally or alternatively, theservice provider may receive payment from the sale of advertisingcontent to one or more third parties.

In one aspect of the present invention, an application may be deployedfor performing one or more aspects of the present invention. As oneexample, the deploying of an application comprises providing computerinfrastructure operable to perform one or more aspects of the presentinvention.

As a further aspect of the present invention, a computing infrastructuremay be deployed comprising integrating computer readable code into acomputing system, in which the code in combination with the computingsystem is capable of performing one or more aspects of the presentinvention.

As yet a further aspect of the present invention, a process forintegrating computing infrastructure comprising integrating computerreadable code into a computer system may be provided. The computersystem comprises a computer readable medium, in which the computermedium comprises one or more aspects of the present invention. The codein combination with the computer system is capable of performing one ormore aspects of the present invention.

Further, other types of computing environments can benefit from one ormore aspects of the present invention. As an example, an environment mayinclude an emulator (e.g., software or other emulation mechanisms), inwhich a particular architecture (including, for instance, instructionexecution, architected functions, such as address translation, andarchitected registers) or a subset thereof is emulated (e.g., on anative computer system having a processor and memory). In such anenvironment, one or more emulation functions of the emulator canimplement one or more aspects of the present invention, even though acomputer executing the emulator may have a different architecture thanthe capabilities being emulated. As one example, in emulation mode, thespecific instruction or operation being emulated is decoded, and anappropriate emulation function is built to implement the individualinstruction or operation.

In an emulation environment, a host computer includes, for instance, amemory to store instructions and data; an instruction fetch unit tofetch instructions from memory and to optionally, provide localbuffering for the fetched instruction; an instruction decode unit toreceive the fetched instructions and to determine the type ofinstructions that have been fetched; and an instruction execution unitto execute the instructions. Execution may include loading data into aregister from memory; storing data back to memory from a register; orperforming some type of arithmetic or logical operation, as determinedby the decode unit. In one example, each unit is implemented insoftware. For instance, the operations being performed by the units areimplemented as one or more subroutines within emulator software.

Further, a data processing system suitable for storing and/or executingprogram code is usable that includes at least one processor coupleddirectly or indirectly to memory elements through a system bus. Thememory elements include, for instance, local memory employed duringactual execution of the program code, bulk storage, and cache memorywhich provide temporary storage of at least some program code in orderto reduce the number of times code must be retrieved from bulk storageduring execution.

Input/Output or I/O devices (including, but not limited to, keyboards,displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives andother memory media, etc.) can be coupled to the system either directlyor through intervening I/O controllers. Network adapters may also becoupled to the system to enable the data processing system to becomecoupled to other data processing systems or remote printers or storagedevices through intervening private or public networks. Modems, cablemodems, and Ethernet cards are just a few of the available types ofnetwork adapters.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiment with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of facilitating replication of data in astorage system, the method comprising: configuring a logical volume of astorage unit of a first storage array of the storage system with atleast one logical volume attribute, the at least one logical volumeattribute comprising a compressible configuration bit indicating whetherall data blocks to be stored to the logical volume are compressibleduring replication thereof to a second storage array of the storagesystem; receiving a data block at the first storage array to be storedto the logical volume of the storage unit of the first storage array;and checking the compressible configuration bit of the at least onelogical volume attribute with which the logical volume is configured,and based thereon, determining whether to compress the data block duringreplication thereof from the first storage array to the second storagearray of the storage system.
 2. The method of claim 1, wherein themethod further comprises replicating the data block from the firststorage array to the second storage array, the replicating comprisingplacing the compressible configuration bit into a data payload region ofa data packet for transmission of the data block from the first storagearray to the second storage array.
 3. The method of claim 2, wherein thereplicating comprises compressing the data block into a compressed datablock at the first storage array and placing the compressed data blockinto the data payload region of the data packet, the compressingoccurring based on the compressible configuration bit indicating thatthe data block is compressible during replication.
 4. The method ofclaim 2, wherein the replicating comprises replicating the data blockfrom the first storage array to the second storage array withoutcompression of the data block based on the checking of the compressibleconfiguration bit indicating that the data block is non-compressibleduring replication.
 5. The method of claim 2, wherein the storage systemfurther comprises a replication link coupling the first storage arrayand the second storage array, and wherein the replicating comprisestransmitting the data packet from the first storage array to the secondstorage array across the replication link.
 6. The method of claim 5,wherein the replication link comprises a Fibre Channel link, and whereinthe placing comprises placing the compressible configuration bit in thedata payload region of the data packet without requiring modification tothe Fibre Channel protocol, wherein the data packet is a Fibre Channeldata packet.
 7. The method of claim 2, further comprising receiving thedata packet at the second storage array, checking the data payloadregion of the data packet for the compressible configuration bit, and ifset, uncompressing the data block at the second storage array, anddiscarding the compressible configuration bit at the second storagearray, and writing the data block to a logical volume of a storage unitof the second storage array.